An Etymological Dictionary of the German Language/Annotated/Harnisch

by Friedrich Kluge

Harnisch, masculine, ‘harness, armour,’ from Middle High German harnasch, variants harnas, harnesch, neuter, ‘harness’; borrowed at the end of the 12th century from Old French harnais, ‘armour, gear,’ which has come to be a common Romance term (Italian arnese), but may be traced probably to a Keltic source (Welsh haiarnaez, ‘iron utensils’); the connecting link might be Middle English harnez, ‘armour’ (English harness).